1. Field of the Invention
The present invention relates to new (2R,4R) monatin monosodium salt hydrate crystals, characterized by having specific, characteristic X-ray diffraction peaks. It also relates to monatin crystals comprising these crystals, and to orally consumed products comprising these crystals.
2. Discussion of the Background
Monatin is a naturally occurring amino acid derivative isolated from the bark of the roots of Schlerochiton ilicifolius, which is a plant naturally grown in the area of northern Transvaal of South Africa. The structure of monatin was reported to be (2S,4S)-2-amino-4-carboxy-4-hydroxy-5-(3-indolyl)-pentanoic acid ((2S,4S)-4-hydroxy-4-(3-indolylmethyl)-glutamic acid) by R. Vleggaar et al. (see, R. Vleggaar et al., J. Chem. Soc. Perkin Trans., 3095-3098 (1992)). The intensity of the sweet taste of the (2S,4S) substance (natural-type monatin) derived from the natural plant is reported in R. Vleggaar et al., J. Chem. Soc. Perkin Trans., 3095-3098 (1992) to be 800 to 1,400-fold that of sucrose. Although various methods of synthesizing monatin have been reported, many of these relate to methods of synthesizing a mixture of stereoisomers. There have been almost no reports in which each of four stereoisomers having the same chemical structural formulae as natural-type monatin is synthesized and isolated as a pure substance and the properties thereof are investigated in detail (see, ZA 87/4288; ZA 88/4220; U.S. Pat. No. 5,994,559; Holzapfel et al., Synthetic Communications, vol. 24 (22), 3197-3211 (1994); and K. Nakamura et al., Organic Letters, 2, 2967-2970 (2000)).
A number of studies have been conducted in recent years into methods of manufacturing monatin (see, WO 2003-056026 and WO 2003-059865). A certain amount of information has been reported on monatin crystals, but much of this relates to potassium salts. There have been only limited reports on sodium salts, which are of the greatest general utility (see, WO 2003-045914, U.S. Published Patent Application No. 2005-272939, Japanese Patent Application Publication No. 2005-154291, and Japanese Patent Application Publication No. 2006-052213). The crystals of the characteristic existing (2R,4R) monatin sodium salt are fine, the salt is difficult to handle, and its thermal stability is somewhat lacking (see, WO 2003-045914).